1. Field of the Invention
The invention relates generally to the field of handheld computers. More particularly, the invention relates to providing a battery power management software for a handheld computer.
2. Description of the Related Art
Most commercial, handheld computers have a built-in battery system. In addition to the battery provided, most handheld computers also have a battery adapter that serves as a battery recharger. The expected usage of a handheld computer is that the operator will use it several times a week, for periods of several minutes at a time. The computer will drain the battery at a moderate rate when the computer is running, and at the self-discharge rate when the computer is shut off. Quite often, the user will use the computer until the “low battery” alarm sounds. At this point, the battery may be drained of 90% of its useful capacity before the user recharges it.
Conventional battery-powered handheld computers provide a single warning message before the primary battery discharges to a cutoff voltage. At the cutoff voltage, the battery-powered computer can no longer be powered by the primary battery and a lockout of applications may occur. The operating voltage of the primary battery discharging below a certain predetermined warning voltage typically triggers the single warning message. Such operating voltage based warning messages can be unsatisfactory due to accuracy limitations of the voltage detection component(s) used to monitor the operating voltage, the warning message is provided too late for the user.
Some conventional battery-powered computers rely on an alternative energy source to ensure retention of data when the energy level of the primary energy source goes below a minimum energy level. These alternative energy sources can include small batteries such as watch batteries, large capacitors, and other energy storage devices. The capacity requirements for the alternative energy sources are typically much lower than the primary energy source capacity. The alternative energy source provides a voltage source when the batteries are replaced. For example, in the Palm III™ handheld computer from Palm Computing, Santa Clara, Calif., a capacitor is charged by the primary energy source (two AAA sized alkaline batteries). The capacitor provides an alternative energy capacity that enables the Palm III™ to retain data for approximately one minute to three minutes without charge from the alkaline batteries, e.g., when the user is replacing the alkaline batteries.
Some prior art devices use secondary or alternate batteries, such as watch batteries. In these devices, the remaining capacity of the alternate battery must be monitored to avoid unpredictable. Monitoring the remaining capacity of the alternate battery is duplicative of any provision to monitor the capacity of the primary battery itself.
Some handheld computers provide a warning that the main battery needs to be recharged and then locks out the hardware of the computer. The charge remaining on the main battery is then used as a capacitor to retain the data in the memory. Typically, the user has 1-2 days to recharge the battery on the computer to avoid loss of stored data.